Modem buildings and building complexes utilize complex building automation and control systems that typically include hundreds of distributed components, controllers, sensors, etc., often from various manufacturers. Such automation and control systems include heating, ventilating, and air-conditioning (HVAC) control, lighting control, access control, and fire detection and suppression systems, etc.
To ensure that these various systems work correctly, it is imperative that the components and controllers utilized in such systems are able to communicate with each other to share information and control signals. If all of the components were sourced from a single manufacturer, such integrated communication, likely from a proprietary communication protocol, would be assured. Unfortunately, this is not the reality in modem systems. As such, it is necessary that, at least externally of the devices themselves, a common communications protocol is used. For the building and automation control market, this common protocol is the Building Automation Control Network (BACnet) communication protocol. Since its development, BACnet has been adopted by the American National Standards Institute (ANSI) as ANSI/ASHRAE Standard 135-1995 and by the International Standards Organization (ISO) as ISO 16484-5 in 2003.
BACnet is a flexible, object oriented approach to communications protocol. It utilizes objects, properties and services to represent data and actions available in the building automation system. Within the BACnet protocol, there are also defined a number of data link/physical layers over which and how communications pass, including ARCNET (ANSI/ATA 878.1), Ethernet, BACnet/IP, Point-To-Point over RS-232, Master-Slave/Token-Passing (MS/TP) over RS-485, etc. With many of these, communications and control timing and communications bandwidth can become problematic as more and more devices are included in the building automation and control system.
As an example, many systems, e.g. in fire control systems governed by Underwriters Laboratory (UL) standard UL 864 Control Units and Accessories for Fire Alarm Systems, there is a requirement for notification of the failure of a component of the system within a certain amount of time. While BACnet provides for a method of determining the operational communication status of a device, requiring the periodic pinging of all system components at a rate to satisfy such a requirement uses up a substantial amount of bandwidth available, particularly when communications occurs over an MS/TP communications bus. This problem becomes acute as the size and complexity of the system grows.
As such, there is a need in the art for a system and method of monitoring the communication status of devices on a BACnet network that allows prompt detection of communications failures without using excessive communications bandwidth. Embodiments of the invention provide such systems and methods. These and other advantages of the invention, as well as additional inventive features, will be apparent from the description of embodiments of the invention provided herein.